The present invention relates to blends of a rubber-modified vinyl chloride resin (PVC), prepared by polymerizing vinyl chloride in the presence of 15 to 30 percent of a rubber, with an unmodified vinyl chloride resin and a polymer of a vinyl aromatic monomer, such as styrene or p-methylstyrene, and an unsaturated dicarboxylic acid anhydride such as maleic anhydride. An optional third monomer may be used in the polymer, such as methyl methacrylate or acrylonitrile, and the polymer may also optionally contain 5 to 25 percent of a rubber grafted with a portion of the polymer. Up to 15 percent of an ungrafted rubber such as a block copolymer of 1,3-butadiene and styrene, or up to 40 percent of a graft copolymer of rubber, styrene, and methyl methacrylate or acrylonitrile may also be added to the blend.
Vinyl chloride resins have good physical properties and generally have good molding characteristics, although the use of a plasticizer and/or a high processing temperature is frequently required (U.S. Pat. No. 3,925,510). However, they have a relatively low softening temperature, e.g. 65.degree.-75.degree. C., and when a large amount, up to about 30 percent, of a relatively low molecular weight plasticizer is added to improve processability and flexibility, the softening temperature may be significantly reduced, e.g. to 60.degree. C. or lower. In the past, various copolymers or terpolymers with higher softening temperatures than a vinyl chloride resin have been blended into the vinyl chloride resin in order to provide good dimensional stability at a higher temperature. The blending of copolymers or terpolymers containing a vinyl aromatic monomer and maleic anhdride, with optionally a third monomer, in order to modify the properties of a vinyl chlorde resin or a graft copolymer of styrene, acrylonitrile, and a butadiene-based rubber (ABS) has been described in various patents.
This earlier work, discussed in detail in my co-pending applications Ser. Nos. 494,708 and 494,709, describes the use of both rubber-modified and unmodified copolymers or terpolymers containing an anhydride such as maleic anhydride, however, emphasis upon use of unmodified vinyl chloride resins was made. This invention discloses the use of such vinyl chloride resins together with rubber-modified vinyl chloride resins prepared by polymerizing vinyl chloride and optional comonomer in the presence of the rubber, in order to obtain a separate rubber phase grafted with a portion of the vinyl chloride polymer. There are distinct advantages in the use of such vinyl chloride resins because of their superior processability and much higher impact strength.
U.S. Pat. No. 3,642,949 describes blends of copolymers of styrene and maleic anhydride (S/MA) with ABS graft copolymers in order to increase the softening temperature of the latter. U.S. Pat. No. 4,339,554 describes blends of rubber-modified or unmodified S/MA copolymers with unmodified vinyl chloride resins. U.S. Pat. No. 4,197,376 describes blends of rubber-modified S/MA copolymers or terpolymers containing up to 30 percent of methyl methacrylate (S/MA/MM) or acrylonitrile (S/MA/AN) with ABS resins.
U.S. Pat. No. 3,626,033 describes blends of unmodified S/MA copolymers, unmodified vinyl chloride resins, and ABS. U.S. Pat. No. 4,329,272 describes blends of unmodified S/MA copolymers, which could optionally contain up to 20 percent of methyl methacrylate or acrylonitrile, with unmodified vinyl chloride resins. The blend could optionally contain up to 40 percent of ABS or MBS (a graft copolymer of styrene, methyl methacrylate, and a butadiene-based rubber). U.S. Pat. No. 4,311,806 describes similar blends in which the maleic anhydride copolymers or terpolymers were rubber-modified.
U.S. Pat. No. 4,454,300 describes blends of a vinyl chloride-polyolefin graft (rubber-modified) copolymer with a copolymer of styrene and maleic anhydride. Preferred polyolefin elastomers were copolymers of ethylene and propylene, or terpolymers containing up to 15 percent of a diene monomer (EPDM). The copolymer could contain up to 25 percent of a third monomer such as acrylonitrile or methyl methacrylate, and could be rubber-modified. These blends exhibited higher heat distortion temperatures than those of the vinyl chloride polymers. The blends could optionally contain acrylonitrile/butadiene/styrene or methyl methacrylate/butadiene/styrene resins.
British Pat. No. 2,015,007, which is incorporated into this disclosure by reference, discloses blends of vinyl chloride resins with block copolymer rubbers of a diene and a vinyl aromatic monomer, together with up to 20 percent of an impact modifier, ABS or MBS. Blends of rubber-modified vinyl chloride resins with block copolymer rubbers were also disclosed, optionally containing ABS or MBS.
Bourland and Wambach (Plastics Engineering, May 1983, p. 23: J. Vinyl Technol., 1983, 5 (3), p. 121) disclosed that S/MA copolymers are partially miscible with vinyl chloride resins and hence, increase the softening temperature and reduce melt viscosity. Impact modifiers could be added to the blends.
Hall, Mendelson, and Trementozzi discussed the preparation of blends of various terpolymers containing maleic anhydride (S/MA/X) with random copolymers of styrene and acrylonitrile (S/AN) or ABS. (See Preprint for Organic Coatings and Plastics Chemistry Division, 47, p. 298, Meeting of the Am. Chem. Soc., Sept. 12-17, 1982).